1. Field of the Invention
This invention is generally related to power-up switch mechanisms in computer systems and more particularly to power-up switch circuits used in peripheral devices and with interface buses.
2. Description of Related Art
Various techniques for controlling electrical power supplied to a computer system have been developed over the years to provide the user with a convenient way to turn on and turn off the computer system. One recent innovation has been to equip a peripheral device such as a keyboard with a switch to control the supply of main power to the desktop computer. This allows the user to easily turn on and turn off the desktop computer while the main processing portion including the motherboard and disk drive is located farther than the user's hand can reach. FIG. 5 shows such a prior art design.
FIG. 5 shows a keyboard 512 equipped with a normally open push-button switch 502 for controlling the power supply to the main processing portion. The conveniently located switch 502 is connected to a dedicated power-on wire 508 which is part of the Apple Desktop Bus.TM. 510 (ADB) that couples the keyboard 512 to the processing portion 514. The bus 510 also includes power, return and data wires that provide power to the keyboard from the main supply (not shown), and transmission of data representing keystrokes on the keyboard. The dedicated power-on wire 508 is not used for data transmission and is biased via a pull-up resistor 504 to a trickle power source. When the user presses the push-button switch 502 in the keyboard, the dedicated power-on wire is connected to common return signaling a desire to turn on or turn off the power. When the push-button switch is depressed again after main power has been turned on, the dedicated power-on wire is once again connected to the common return.
A problem with the prior art design in FIG. 5, however, is that a dedicated wire is required for controlling the power. Modern and future computer peripheral interface bus standards, however, do not always provide for a dedicated power-on wire. These include, for instance, the Universal Serial Bus (USB) which only defines data, power, and return wires as part of the peripheral interface bus. Therefore, what is needed is a novel design for controlling power in computer systems which does not require a dedicated wire as part of the interface bus.